Rho-Kinase (ROCK) is a member of the serine-threonine protein kinase family. ROCK exists in two isoforms, ROCK1 and ROCK2 (T. Ishizaki et al., EMBO J., 1996, 15, 1885-1893). ROCK has been identified as an effector molecule of RhoA, a small GTP-binding protein (G protein) that plays a key role in multiple cellular signaling pathways. ROCK and RhoA are ubiquitously expressed across tissues. The RhoA/ROCK signaling pathway is involved in a number of cellular functions, such as actin organization, cell adhesion, cell migration, and cytokinesis (K. Riento and A. J. Ridley, Nat Rev Mol Cell Biol, 2003, 4, 446-56). It is also directly involved in regulating smooth muscle contraction (A. P. Somlyo, Nature, 1997, 389, 908-911). Upon activation of its receptor, RhoA is activated, and, in turn, it activates ROCK. Activated ROCK phosphorylates the myosin-binding subunit of myosin light chain phosphatase, which inhibits activity of the phosphatase and leads to contraction. Contraction of the smooth muscle in the vasculature increases blood pressure, leading to hypertension.
There is considerable evidence in the literature that the Rho A/ROCK signaling pathway plays an important role in signal transduction initiated by several vasoactive factors, for example angiotensin II (T. Yamakawa et al., Hypertension, 2000, 35, 313-318), urotension II (V. Sauzeau et al., Circ. Res., 2001, 88, 1102-1104), endothelin-1 (P. Tangkijvanich et al., Hepatology, 2001, 33, 74-80), serotonin (H. Shimokawa, Jpn. Circ. J., 2000, 64, 1-12), norepinephrine (M. C. Martinez, et al., Am. J. Physiol., 2000, 279, H1228-H1238) and platelet-derived growth factor (PDGF) (H. Kishi et al., J. Biochem., 2000, 128, 719-722). Many of these factors are implicated in the pathogenesis of cardiovascular disease.
Additional studies in the literature, some using the known ROCK inhibitors fasudil (T. Asano et al., J. Pharmacol. Exp. Ther., 1987, 241, 1033-1040) or Y-27632 (M. Uehata et al., Nature, 1997, 389, 990-994) further illustrate the link between ROCK and cardiovascular disease. For example, ROCK expression and activity have been shown to be elevated in spontaneously hypertensive rats, suggesting a link to the development of hypertension in these animals (Y. Mukai et al., FASEB J., 2001, 15, 1062-1064). The ROCK inhibitor Y-27632 (M. Uehata et al., Nature, ibid) was shown to significantly decrease blood pressure in three rat models of hypertension, including the spontaneously hypertensive rat, renal hypertensive rat and deoxycortisone acetate salt hypertensive rat models, while having only a minor effect on blood pressure in control rats. This reinforces the link between ROCK and hypertension.
Other studies suggest a link between ROCK and atherosclerosis. For example, gene transfer of a dominant negative form of ROCK suppressed neointimal formation following balloon injury in porcine femoral arteries (Y. Eto et al., Am. J. Physiol. Heart Circ. Physiol., 2000, 278, H1744-H1750). In a similar model, ROCK inhibitor Y-27632 also inhibited neointimal formation in rats (N. Sawada et al., Circulation, 2000, 101, 2030-2033). In a porcine model of IL-1 beta-induced coronary stenosis, long term treatment with the ROCK inhibitor fasudil was shown to progressively reduce coronary stenosis, as well as promote a regression of coronary constrictive remodeling (H. Shimokawa et al., Cardiovascular Res., 2001, 51, 169-177).
Additional investigations suggest that a ROCK inhibitor would be useful in treating other cardiovascular diseases. For example, in a rat stroke model, fasudil was shown to reduce both the infarct size and neurologic deficit (Y. Toshima, Stroke, 2000, 31, 2245-2250). The ROCK inhibitor Y-27632 was shown to improve ventricular hypertrophy, fibrosis and function in a model of congestive heart failure in Dahl salt-sensitive rats (N. Kobayashi et al. Cardiovascular Res., 2002, 55, 757-767).
Other animal or clinical studies have implicated ROCK in additional diseases including coronary vasospasm (H. Shimokawa et al., Cardiovasc. Res., 1999, 43, 1029-1039), cerebral vasospasm (M. Sato et al., Circ. Res., 2000, 87, 195-200), ischemia/reperfusion injury (T. Yada et al., J. Am. Coll. Cardiol., 2505, 45, 599-607), pulmonary hypertension (Y. Fukumoto et al., Heart, 2005, 91, 391-392), angina (H. Shimokawa et al., J. Cardiovasc. Pharmacol., 2002, 39, 319-327), renal disease (S. Satoh et al., Eur. J. Pharmacol., 2002, 455, 169-174) and erectile dysfunction (N. F. Gonzalez-Cadavid and J. Rajifer, Endocrine, 2004, 23, 167-176).
In another study, it has been demonstrated that inhibition of the RhoA/ROCK signaling pathway allows formation of multiple competing lamellipodia that disrupt the productive migration of monocytes (R. A. Worthylake et al. The Journal of Biol. Chem., 2003, 278, 13578-13584). It has also been reported that small molecule inhibitors of Rho Kinase are capable of inhibiting MCP-1 mediated chemotaxis in vitro (H. Iijima, Biorganic and Medicinal Chemistry, 2007, 15, 1022-1033). Due to the dependence of immune cell migration upon the RhoA/ROCK signaling pathway one would anticipate inhibition of Rho Kinase should also provide benefit for diseases such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease.
The above studies provide evidence for a link between ROCK and cardiovascular diseases including hypertension, atherosclerosis, restenosis, stroke, heart failure, coronary vasospasm, cerebral vasospasm, ischemia/reperfusion injury, pulmonary hypertension and angina, as well as renal disease and erectile dysfunction. Given the demonstrated effect of ROCK on smooth muscle, ROCK inhibitors may also be useful in other diseases involving smooth muscle hyper-reactivity, including asthma and glaucoma (H. Shimokawa et al., Arterioscler. Thromb. Vase. Biol., 2005, 25, 1767-1775). Furthermore, Rho-kinase has been indicated as a drug target for the treatment of various other diseases, including airway inflammation and hyperresponsiveness (P. J. Henry et al., Pulm Pharmacol Ther., 2005, 18, 67-74), cancer (R. Rattan et al., J. Neurosci. Res., 2006, 83, 243-55. D. Lepley et al., Cancer Res., 2005, 65, 3788-95), fibrotic diseases (C. Jiang, et. al., Int. J. Mol. Sci., 2012, 13, 8293-8307; L. Zhou, et. al., Am. J. Nephroi., 2011, 34, 468-475), as well as neurological disorders, such as spinal-cord injury, Alzheimer disease, multiple sclerosis, stroke and neuropathic pain (B. K. Mueller et al., Nat Rev Drug Disc, 2005, 4, 387-398; X. Sun et. al., J. Neuroimmunology, 2006, 180, 126-134).
There remains an unmet medical need for new drugs to treat cardiovascular disease. In the 2012 update of Heart Disease and Stroke Statistics from the American Heart Association (Circulation, 2012, 125, e2-e220), it was reported that cardiovascular disease accounted for 32.8% of all deaths in the US, with coronoary heart disease accounting for ˜1 in 6 deaths overall in the US. Contributing to these numbers, it was found that ˜33.5% of the adult US population was hypertensive, and it was estimated that in 2010 ˜6.6 million US adults would have heart failure. Therefore, despite the number of medications available to treat cardiovascular diseases (CVD), including diuretics, beta blockers, angiotensin converting enzyme inhibitors, angiotensin blockers and calcium channel blockers, CVD remains poorly controlled or resistant to current medication for many patients.
Although there are many reports of ROCK inhibitors under investigation (see, for example, U.S. 2008/0275062 A1), fasudil is the only marketed ROCK inhibitor at this time. An i.v. formulation was approved in Japan for treatment of cerebral vasospasm. There remains a need for new therapeutics, including ROCK inhibitors, for the treatment of cardiovascular diseases, cancer, neurological diseases, renal diseases, fibrotic diseases, bronchial asthma, erectile dysfunction, and glaucoma.